In recent years, in the field of image display device for displaying images, organic EL display devices having a number of pixel circuits, containing an electro luminescence element, i.e., organic EL element, which is a so-called current-driven electro-optical element whose light emission brightness changes in accordance with current value flowing through the element, arranged in a matrix form have been developed and commercialized.
An organic EL element is self-luminous. As a result, an organic EL display device offers several advantages compared with a liquid crystal display device which controls the light intensity from the light source (backlight) by means of pixels, containing liquid crystal cells such as high image visibility, no need for backlight and high response speed of the element.
An organic EL display device can employ either a simple (passive)-matrix system or an active-matrix system driven as with a liquid crystal display device. It should be noted, however, that a simple matrix display device has some problems although simple in construction. Such problems include such as difficulty in implementing a large high-definition display device.
For this reason, in recent years, the development of active matrix display devices has been going on at a brisk pace. Such display devices control the current flowing through the electro-optical element with an active element such as insulating gate field effect transistor (typically, thin film transistor; TFT) provided in the same pixel circuit as the electro-optical element.
In an active matrix organic EL display device, a pixel (pixel circuit) at least includes, in addition to an organic EL element, a drive transistor adapted to drive the organic EL element, a write transistor adapted to sample an input signal voltage and write the voltage to the pixel, and a holding capacitance connected to the gate of the drive transistor to hold the input signal voltage written by the write transistor (refer, for example, to Japanese Patent Laid-Open Publication No. 2005-345722).